Rubber stabilization with monohydroxy phenol-indene or coumarone alkylation product



United States RUBBER STABILIZATION WITH MON OHYDROXY PHENOL-INDENE ORCOUMARONE ALKYLA- TION PRODUCT No Drawing. Filed June 25, 1957, Ser. No.667,972

16 Claims. (Cl. 260-4595) This invention relates to a process forprotecting rubber by means of a compounding agent having antioxidantproperties, and to rubber containing said agent. More particularly, itrelates to the inhibition of oxidation and aging of rubber by means ofpolysubstituted products of phenols and indene, coumarone, methylindenes, methyl coumarones, and mixtures thereof.

A wide variety of compounds have been proposed for use as antioxidantsin natural and synthetic rubbers and mixtures thereof. The use ofantioxidants is so common as to require little comment. In general anantioxidant should not interfere or alter substantially, the curingcharacteristics of the rubber composition and should be capable ofinhibiting the aging of the rubber in the presence of ultraviolet lightand/or oxygen at the tempera tures normally encountered under serviceconditions. They should not migrate or cause bloom or frosting, and withlight colored rubber compositions should not develop stain or darkeningdue to exposure to oxygen, ultraviolet light and heat. Moreover,antioxidants should not impart stain upon contact.

The compounds with which this invention is concerned meet theserequirements to an extent equal to and in some cases superior tocompetitive antioxidants which have had Wide commercial acceptance.

The compounds are prepared from phenols such as the mixed commercialcresylic acids by reaction with naphthas containing indene as theprincipal polymerizable component, but which may include coumarone andthe lower alkyl derivatives of coumarone and indene. Such naphthas arederived from coal tar, drip oil from manufactured gas processes, or fromsevere thermal cracking of petroleum gas oils, or other sources. Pure orsubstantially pure indene may be used. Pure or substantially pu-rephenol, cresols, and xylenols may also be used.

' The condensation products may be prepared by reacting the cresylicacids and the indene-containing naphthas in the presence of a catalystsuch as acidic clays or those comprising Friedel-Crafts type or theircomplexes with acids, usually in the presence of an aromatic solvent.

"atom which can be removed from the final product .by distillation at atemperature of about 150 C. to about 250 C., for a period of time suchthat the reaction is com- "ice of the naphtha. (The polymerizableportion of the naphtha is defined as that portion of the naphtha whichis convertible to resins of the coumarone-indene type by the usualsulfuric acid polymerization method.) The naphthas boil in the range ofabout 160200 C. and contain upwardsof about 40% indene.

When the reaction is complete the solvent, if any, is removed bydistillation at atmospheric pressure. The residue is then subjected tovacuum or steam distillation. to remove a liquid product comprisingprimarily phenols alkylated with two indene groups, there possibly beingsmall quantities of tri-substituted phenols present. The averagemolecular weight of the oil is in the neighborhoodo-f about 250 or 300.The oil has a light amber color and is cut to an initial boiling pointof about 300 C. or higher.

The residue is a solid which when viewed in the massive state is lightamber color and may have a melting point from about 50 C. to about 100C. or higher. This depends upon how much of the oily product is removedby distillation. Ordinarily the residue is distilled-to a melting pointof about 65 C. to about C. It may have an average molecular weightupward from about 375, say about 400 to about 800' or more. One of theproducts is a liquid and the other is a solid and they are not exactlyequivalent. The structural composition is believed to include thefollowing where R is a radical selected from the group consisting. ofindene, coumarone, and their methyl substituted homologs or their dimersor trimers such as diindene or dicoumarone; and R' is hydrogen or a lowmolecular weight alkyl group containing 1 to 3 carbon atoms; and where nis a whole number equal to at least 2 where R is a monomer; or at least1 where R is a dimer or trimer; and n is a small Whole number from 0-3.R is attached at the a or ,8 position of the 5-membered ring either byaddition or substitution; i.e. with or without two unsaturated doublebonds in the 5-membered ring in the final alkylate.

They are compounded with either natural or synthetic rubber or mixturesthereof in the usual manner by mixing the antioxidants into thecompounded rubber in proportions of about 0.5% to about 5% by weight andpreferably about 0.75% to about 2% by weight of the rubber. They areeffective non-staining, non-discoloring antioxidants which do not aifectthe curing or vulcanizing characteristics of the rubber, and which areat least as effective in preventing adverse oxidation and aging effectsas are presently available commercial antioxidants as is shown by thefollowing examples.

EXAMPLE I The antioxidant used in this example (Product 1) was a liquidprepared as described above which had a Gardner color of less than 9;specific gravity at 30 C. of 1.08 to 1.09; flash point by the ClevelandOpen Cup method above 275 F.; and viscosity (S.S.U. at 210 F.) 50-60. Itwas soluble in a variety of solvents including acetic acid, acetone,aliphatic hydrocarbons, aro

matic hydrocarbons, carbon tetrachloride, dioxane, ethyl acetate,ethylene glycol, gasoline, methanol, etc.

As an example of the age-retarding efiect and physical propertiesresulting from the use of Product 1, the following natural rubber stockwas prepared. The proportions are, in parts by weight The samples cured40 minutes at 274 F. were placed between two white Dulux coated panelsand exposed in the hot air oven for 48 hours at 70 C. under a five poundload to determine contact staining. Both of the Pale crepe rubber 100.00antioxidant containing stocks showed only very slightly A zO ZZZ5 5 zincoxide 50.00 more staining than the control. Tltanfum fllOXlde ALO -00The above data show that Product 1 antioxidant gives Steal-1c. acidequal non-staining results and better protection other- Ultramanne blue:0-125 wise than a commonly used non-staining antioxidant.Mercaptobenzothmzole 1.00 10 Sulphur 3.00 EXAMPLE II Antioxidant (whereused) 1.00 Using this recipe Product 1 was compared with a well This P'oduct 2 was the normally solid resin produced known non-stainingantioxidant and a control containing 1 as descnbed above' It was hghtamber color had no antioxidant. Since the curing rates at 20, and 5 ameltlng P y he c pillary method above minutes at 274. c were practicallyequal, the values and has spec1fic gravity at 25/25 C. of 1.137. ThlS ofthe physical properties were. averaged for clearer pmdllct.ls Soluble111 the usual rubber Solventsanalysis. Results are as follows: It wastested in a natural rubber composition formu- UNAGED Modulus Tensile,Elonga- Antioxidant Lbs/Sq. tion, Set, Per- Hardness T 50,0. SpecificIn. Percent cent Shore A Gravity 200% 500% 1 Commercial antioxidant. Thesame stocks were treated in an oxygen bomb for lated as shown in ExampleI, and in like proportions. 96 hours/3005 O 80 C. and then tested atroom tem- Product 2' was compared in this test compound with perature.The average aged physicals for the 30, 40, a well-known non-staining,non-discoloring antioxidant and 60 minute cures are as follows: enjoyinglarge volume commercial usage. A control AGED Modulus Percent ofTensile, Elonga- Percent Original Antioxidant Lbs/Sq. tion, Set, Per-Hardness Wt.

In. Percent cent ShoreA Increase 200% 500% Tensile Elen gation 1Commercial antioxidant. 5 An ultraviolet discoloration test was thenmade on containing no added antioxidant was also used for comsamples ofstock cured 40 minutes at 274 F., using parison. Since graphs of theT-50 data showed the exposure periods of 4, 8, and 12 hours in theWeatherequivalent test values to be within less than 210% O-Meter (nospray). The stocks containing Product 1 50 of 35 'minutes at 274 F., thephysicals for the 30-, and the other antioxidant discolored only veryslightly 40-, and 60-minute cures were averaged for a better as comparedwith the control stock containing no antianalysis of the propertiesdeveloped. These averages oxidant. are shown.

UNAGED Modulus Tensile, Elonga- Antioxidant Lbs/Sq. tion Set,Per-Hardness, Specific In. Percent cent ShoreA Gravity Product2 230 11203240 735 28 .42 1.403 31.0. 245 1305 8180 705 28 44 1.398 None 270 12953345 715 27 44 1.403

Commercial Antioxidant.

. AGED [Oxygen bomb 96 hours/300 13.5.1. 01/80 0. (ASTM D-412 andD-572)] V Modulus 1 Percent of Tensile, Elonga- Percent OriginalAntioxidant Lbs/Sq. tion, Set,Per- Hardness, Weight In. Percent centShoreA Increase 200% 500% Tensile 'Elon- V gation CommercialAntioxidant.

Discoloration test.-Ultraviolet exposure discoloration was determined inthe Weather-O-Meter, without spray, at 4, '8, and 12 hours. Theinhibited specimens were all in the non-discoloring class with slightdiiterences, if any, between them. Product 2 was, therefore, the equalof presently acceptable commercial antioxidants. Test proceduresemployed were as follows:

Physical state of cure of vulcanized rubber (T-SO test) ASTM D599-4OT.Tension testing of vulcanized rubber ASTM D412-51T.

EXAMPLE III Product 1 emulsions The formulations shown below shouldserve as excellent staring points for the emulsification and dispersionof Product 1 in many commercial applications, particularly in rubberlatex compounding work:

Component: Parts by weight Product 1 5O Oleic acid 3.0 Ammoniumhydroxide (NH OH) (28% NH 0.8 Water, distilled 20 Component: Parts byweight Product 1 50 Aerosol OT, 75% (anionic) 2 Tergitol NPX (nonionic)2 Water, distilled l7 'Jlrademark, American Cyanamid Co., sulfonateddisarboxylic acid.

'lrademark, Carbide & Carbon Chemical Corp., alkyl phenyl ether ofpolyethylene glycol.

Mixing pr0cedure.Both of the Wetting agents are added to the Product 1.The water is then slowly added to the oil in small portions withmechanical agitation. A water-in-oil emulsion forms which, upon thefurther addition of water, inverts to the oil-in-water type. Again,thinning water can be added as desired. This emulsion is quite stableand shows a pH of about 8 to pH paper. To prepare a more highly alkalineemulsion of this type, it is only necessary to add about 0.5 pt. NH OHto the water before its addition to the oil. As a result of the nonionicagent present, this system may not be as desirable as the first emulsionsystem in rubber latex work, but is useful in other systems.

The first of the above emulsions was mixed with rubber latex inproportions of 1, 2 and 3 parts (of solids) per 100 parts of naturalrubber hydrocarbon. They were compared with a commercial widely usedantioxidant in this service (adhesive compositions). The inhibited samples were cast on sheets of polyvinyl chloride. In 7 day aging tests atroom temperature the Product 1 samples were lighter than lthecommercialantioxidant. In 'ultra' violetitests (20 hours) the control was verytacky, and the Product 1' sample was less so than the commercialantioxidant sample.

' In none of 'these tests, including the 5 day oven tests at 50 0., didthe Product 1 or the commercial antioxidant stain the substrate. Product1 rates as a non-staining, non-discoloring antioxidant of equal orsuperior properties to the commercial antioxidant.

Product 2 dispersions A The formulations shown below are dispersions ofProduct 2 useful in many'commercial applications, particularly rubberlatex compounding work:

Component; Parts by weight Product 2 45 Methocel (400 cps.),'3% solution30 Tamol 731, 25% (anionic) 2 Water, distilled 2 l 'lrademark, DowChemical C0,, methyl cellulose.

3 Trademark, Rohm & Haas, sodium aryl sulfona'te.

Mixing procedure.-The Tamol 731 and Methocel solution are added to thepulverized Product 2. The resultant slurry is given two passes through athree-roll paint mill with the remainder of the water being added on themill.

Component: Parts by weight Product 2 50 Darv an No. l (anionic) 2.0

, Burtonite X- 0.7

1 Water, distilled 48 1 Trademark, R. T. Vanderbilt Company, Inc.

a Trademark, Burtonite Company.

Mixing procedure-The Burtonite X-9O is slowly sifted into the Water withmechanical agitation. Stirring is continued until a uniform mixture isobtained (about 15 to 20 minutes). The Daryan No. 1 is then added to thewater phase with continued stirring. The water mixture is added to thepowdered Product 2. The resultant slurry is then given two passesthrough a three-roll paint mill. This finished dispersion is viscous butstable. Similar results can be obtained by ball milling all of theingredients for an estimated 24 to 48 hours.

The foregoing examples are given to illustrate the invention but are notintended to restrict it to the exact conditions shown.

I claim as my invention:

1. A process for inhibiting the oxidation and aging of rubber whichcomprises compounding said rubber with a small but effective amount of acompound prepared by alkylating a monohydroxy phenol having thestructure where R is a low molecular weight alkyl group having from 1 to3 carbon atoms and n is a small whole number of 0-3, with a compound, R,selected from the group consisting of indene, coumarone, their methylsubstituted homologs, their dimers and trimers, and combinations of saidcompounds, to yield a product consisting essentially of an alkylatedphenol having a molecular weight of at least 250 and an initial boilingpoint of at least about 300 0., having the structure the phenyl groupbeing attached to the five membered ring of the group R, and where n, isat least 2 when R is a monomeric group and at least 1 when R is a dimerortrimer. I

2. The process vof claim 1 wherein R is attached at them position of the5 membered ring. l

3. The process of claim 1 wherein R is attached at the 8 position of the5 membered ring. 1

4. The process of claim 1 wherein R is indanyland n is at least 2. t

5. The process of claim 1 wherein R is a diindanyl radical and n is atleast 1. I

6. The process of claim 1 wherein the antioxidant is the alkylationproduct of' cresylic acid and an indene containing naphtha. Y

7. A stabilized rubber composition containing from about 0.5% to about5% by weight; of an antioxidant comprising a substituted phenol preparedby alkylating a monohydroxy phenol having the structure where R is a lowmolecular weight alkyl group having from 1 to 3 carbon atoms and n is asmall whole'number of 0-3, with a compound R, selected from the groupconsisting of indene, coumarone, their methyl substituted homologs,their dimers and trimers, andcombinations of said compounds, to yield aproduct consisting essentially of an alkylated phenol having amolecular'weight of at least 250 and an initial boiling pointoi at leastabout 300 0, having the structure I a the phenyrgroup being attached tothe five membered ring of the group R, and where n is at least 2 when Ris a monomeric group and at least 1 when R is a dimer or trimer. r

8. The composition of claim 7, wherein R is attached at the a positionof the 5 membered ring;

9. The composition of claim 7 wherein R 1s attached at the p position ofthe 5 membered ring.

10. The composition of claim 7 wherein and n is at least 2. l t

11. The composition of claim 7 wherein R is a diindanyl radical and n1is at least 1. l V

12. The composition of claim 7 wherein the anti oxidant is thealkylation product of cresylic acid and a indene-containing naphtha.

13. The composition. of claim 7 wherein the antioxidant is normallyliquid having an average molecular weight'above about 250. k

' 14. The composition of claim 7 wherein the antioxidant is normallysolid. v

15. The composition of claim 7 wherein the antioxidant is the normallyliquid alkylation product of cresylic acid and an indene-containingnaphtha.

16. The composition of claim 7 wherein the antioxidant is the normallysolid alkylation product of cresylic acid and an indene-containingnaphtha.

R is indanyl References Cited in the file of this patent V UNITED STATESPATENTS 1,754,052 Roseuthal Apr. 8, 1930 1,842,989 Kropp Jan. 26, 19322,109,015 Niederl Feb.'22, 1938 2,606,886 Amberg -L. Aug. 12, 1952

7. A STABILIZED RUBBER COMPOSITION CONTAINING FROM ABOUT 0.5% TO ABOUT5% BY WEIGHT OF AN ANTIOXIDANT COMPRISING A SUBSTITUTED PHENOL PREPAREDBY ALKYLATING A MONOHYDROXY PHENOL HAVING THE STRUCTURE